External sources of water entering a sanitary sewer system is problematic worldwide. For example, when groundwater infiltrates the sanitary sewer system an associated water treatment system may become overtaxed, since it must handle the added water. Since groundwater does not generally need to be treated, this often leads to wasteful increases in processing costs and equipment costs.
In addition, when the demand placed upon the sanitary sewer collection system exceeds its capacity sewage at the treatment facility may prematurely overflow into the environment prior to being fully treated. Likewise, overtaxed sewer systems may hydraulically back up into customers' residences and businesses, often causing overflow of untreated sewage directly into waterways. This is due to the treatment system being forced to convey and treat more water than its intended design capacity. This is a growing problem, particularly as infrastructures age and sewer systems become more porous to the environment.
Groundwater or rainwater entering the sanitary sewer system, commonly referred to as infiltration/inflow (“I/I”), may result from a number of events, such as heavy rains, either locally or remotely (i.e., upstream), flooding, melting snow/ice, and water line breaks, hereinafter referred to as “I/I events.” In this context, groundwater is not necessarily emanating from the ground; rather, it is filtering through the ground and into the sewer system. This water is drawn by gravity to its lowest point, through one or more leaks within the sanitary sewer system, if available. The source of I/I into the sanitary sewer system may include defects in one or more of main lines, lateral lines and manholes. In particular, some of the sources of I/I in a sanitary sewer system include, but are not limited to, pipe cracks, poor pipe joints, poor lateral or manhole pipe connections, and defects in manholes walls, joints, castings, and lids.
There are a multitude of sources of I/I into a sanitary sewer system that ultimately flow to an associated wastewater treatment plant, causing treatment plant capacity problems. Generally, the intensity and duration of rainfall, along with existing groundwater conditions, dictate the amount and intensity of I/I. Typically, the gravity main line sewer, lateral sewers and manholes are all installed on a gravel foundation and are buried within gravel. A consequence of this arrangement is that the gravel provides a pathway for the water to flow by gravity, following the path of least resistance, to the various leakage defects within the sanitary sewer system that act as sources for I/I.
Currently, locating these costly leaks relies much on happenstance, such as someone being in the right place and at the right time to observe a leak during an active I/I event. However, humanly-observed I/I occurrences in real-time are relatively rare; accordingly, many leaks may continue unabated for years before they are detected, if ever.
If an I/I leak is detected it may be readily repaired using any number of suitable remedial measures, such as grouting, surface coatings, lining sewer pipes, replacing faulty pipes, and so on. The challenge facing sewer maintenance personnel is detecting and locating the leaks, which usually occurs only during an I/I event. Adding to the detection problem is a timing element, as some leaks may not occur until days following the rain event because of the distance of the defect from the I/I event, among other factors.
Previous methods for detecting and isolating points of I/I into a sanitary sewer system typically rely solely on visual identification. Consequently, such methods are difficult to perform, are time-consuming, and are expensive. One example of a current process for finding defects in sewer pipe is disclosed in U.S. Pat. No. 4,373,381 to Kulp et al. The process taught by Kulp requires sealing off the incoming pipes and performing a vacuum test on the manhole, which can be both complex and time-consuming. Another relatively complex and time-consuming process for locating defects in pipes involves installing a plug between two sections of pipe to form a seal. A section of the pipe is then pressure tested, as disclosed in U.S. Pat. No. 5,467,640 to Salinas.
Yet another process for finding I/I defects in pipes is disclosed in U.S. Pat. No. 6,621,516 to Wasson et al., which requires flooding the ground surrounding the pipe with phosphorescent dye and detecting the dye as it leaks into the pipe. This process requires substantial amount of time and is not necessarily indicative of the real-world characteristics of what occurs in a sewer system during a rain or I/I event. Wasson, et al., also disclose coating the inside of the pipe with a lacquer coating that is laced with ferromagnetic phosphorescent particles to indicate small cracks or other defects in a pipe when viewed under a black light illuminator. However, the existence of such defects does not necessarily mean that the defects are a source where actual I/I enters the pipe or manhole. Consequently, this can lead to costly and unnecessary repairs.
What is needed is a relatively simple system and method for indicating sources of I/I into a sanitary sewer system that will continue to indicate for some time after the event whether the I/I entered the sewer system at these various defects, to eliminate the need to be physically present and visually observe the I/I occurring.